1. Field of the Invention
The present invention relates to a conveyor for conveying piece goods and the like through a helical path in an upright direction, comprising a frame, an endless conveyor belt supported by the frame and driven by driving means and having a conveying part guided in the helical path and a return path. The conveyor belt includes substantially rigid slats movably coupled near their axis and has an upper transport face, the slats being relatively pivotable both around a first axis parallel to the transport face and perpendicularly to the conveying direction and around a second axis perpendicularly to the transport face and perpendicularly to the conveying direction, the frame comprises a helical support face for slidably supporting the slats in the conveying part, and the frame further comprises a radially directed guide face for guiding these slats substantially radially in the conveying part.
2. Description of the Related Art
Such conveyors are known from practice in various embodiments. For bridging a relatively large height without an overly large pitch of the windings of the helix, it is necessary to use a great number of windings This causes drive problems, however, since the pull forces necessary for moving the belt increase exponentially with the increase of the arc of the belt around the axis of the helix. The resistance experienced by the slat in the conveying direction is, first of all, the result of the frictional forces between the slat and the support face. Secondly, the resistance is caused by the frictional force created by the force with which the slat is urged against the radially directed guide face. This latter force increases exponentially with the length of the arc and thus with the number of windings, and this is the so-called xe2x80x9cnoose effectxe2x80x9d in which the belt is jamming when driven in a pulling fashion.
In practice this problem has tried to be solved by building in auxiliary drives in several positions along the helix. Of course, this results in a substantial increase of the cost price of the conveyor, whereas the reliability and the noise and vibration level are also affected. Another solution for the problem has been sought in using a roller car under each relatively wide slat. These roller cars are equipped with three or four rollers directed radially with respect to a guide tube, the rollers guiding the slats both vertically and horizontally. The disadvantage of this solution is the complexity and the creation of large spaces between the slats at the position of the end pulleys, since the bending center of the conveyor belt (at the point of engagement of the chain) is at a large distance from the transport face of the slats. This makes the conveyor useless for conveying smaller and/or weaker products. It is also impossible to build this prior art conveyor in a compact manner, and the stability of the slats is defective as a result of the roller cars, whereas the chain tension is necessary for the stability.
The object of the present invention is to provide a conveyor with which the above problems are removed in an effective way.
For this purpose, the conveyor according to the invention is characterized in that at least a number of slats are provided with at least a guide roller rotatable about an axis of rotation parallel to the second axis and adapted to roll along the radially directed guide face.
Due to this feature, the xe2x80x9cnoose effectxe2x80x9d as mentioned before is substantially reduced because the frictional forces against the radially directed guide face are at a much lower level due to the rolling friction instead of sliding friction in the prior art. This enables the conveyor belt to be transported through a great number of windings without really necessitating auxiliary drives. Furthermore, the structure can remain simple since only a roller is used for guiding along the regularly directed guide face, whereas the support of the slats by the support face remains a sliding support. If a chain is used as connecting element between the slats, it may engage closely under the transport face of the slat, resulting in a small distance of the bending center of the conveyor belt under it, which causes hardly any spacings between the slats at the end pulleys.
Due to the simple structure the invention may be combined with narrow slats enabling the use of a compact end pulley, which facilitates the incorporation of the conveyor and creates a better transfer to connecting conveyors. The narrow slats also lead to a smaller spacing at the end pulley, whereas also a smaller spacing is created between the slats when they are pivoted relatively in the helical section. Smaller slats are also less inclined to form steps as a result of the inner inclination being steeper than the outer inclination of the helical path.
If a cylindrical guide roller and a vertical smooth guide face are used, no axial loads and no force increases due to resolved forces in the axial direction are created.
The invention will hereafter be further explained with reference to the drawings, showing embodiments of the conveyor according to the invention by way of example.